Supplement Abstract Families caring for people living with Alzheimer?s Disease or related dementias (AD/ADRD) provide more than 90% of the long-term care to individuals living with this complex chronic condition. Family caregivers (CGs) typically assume care responsibilities without training or support and may in turn experience multiple health risks themselves including depression and distress. Identifying innovative approaches for reaching this large population and providing evidence-based supportive programs to enhance their well-being is a public health imperative. One approach to reach AD/ADRD CGs is to augment existing community-based services with an evidence-based program. Adult day service (ADS) is one such growing and critical community-based option that AD/ADRD CGs of older adults rely upon. ADS programs offer out-of-home, supervised activities but do not routinely provide evidence-based supportive CG programs nor tailored recommendations to manage the daily challenges of AD/ADRD. Also ADS use is not consistently associated with reductions in CG depressive symptoms, client dementia-related behavioral symptoms and nursing home admissions. Thus, ADS is an ideal ?test bed? for translating a proven intervention for dementia CGs to reach and support this population. We previously developed and evaluated in a small trial, ADS Plus, a program augmenting ADS with systematic support (e.g., education, skill building) to CGs of clients with AD/ADRD. We showed that ADS Plus in comparison to usual ADS, reduced CG depression and nursing home placement. In response to NIA PA-14- 161 calling for translational research to integrate evidence-based models into existing services, we propose a practical trial design to assess the effectiveness and uptake of ADS Plus on a large scale. We will involve 30 plus ADS programs throughout the U.S. varying in geographic location and staffing levels and 300 CGs (150 in ADS Plus sites; 150 in ADS usual care sites) of persons living with AD/ADRD. We will use cluster and re-randomization techniques, mixed methods, and cost analyses to rigorously evaluate program effectiveness and implementation processes. If effective, and with consultation from a Translation Advisory Board of key ADS leaders, ADS Plus will be disseminated widely. Primary study aims are to: 1) evaluate the effectiveness of ADS Plus to improve CG well-being and reduce depressive symptoms compared to routine ADS use at 6 months (Hypothesis 1: CGs of persons living with AD/ADRD using ADS Plus will report improved well-being and reductions in depressive symptoms compared to those in routine ADS only); and 2) evaluate long-term maintenance effects of ADS Plus at 12 months on CG well-being and depressive symptoms (Hypothesis 2: CGs of persons living with AD/ADRD using ADS Plus will maintain benefits from 6 to 12 months). Additional study aims will: 3) evaluate whether CGs using ADS Plus are more likely to maintain relatives with AD/ADRD in ADS and less likely to place them in residential settings compared to those in routine ADS over 12 months; 4) estimate ADS Plus costs and assess whether it results in net financial benefits when compared to usual ADS at 6 and 12 months; 5) evaluate the effects of ADS Plus on client behaviors and CG efficacy and upset managing symptoms; and 6) evaluate theoretically-derived (RE-AIM, Stress Process Model) mediational pathways of treatment change including CG acceptance and staff adoption of ADS Plus over 12 months.